1. Field of the Invention
This invention relates to reciprocating pump packings and more particularly to such packings particularly adapted for use under conditions causing severe wear problems.
2. Description of the Prior Art
Pump packings made from a stack of fabric reinforced uncured rubber disc preforms have long been in use in reciprocating pumps such as those manufactured by FMC Corporation, Agricultural Machinery Division, Jonesboro, Ark. The packing is generally in the shape of a spherical cup having a forward annular lip which is compressed somewhat when fitted within the walls of a pump cylinder. The cup is formed under heat and pressure with the rearmost disc in the stack becoming the convex surface of the packing and terminating at the forward annular lip. Thus, the rearmost disc in the stack is the only disc which contacts the cylinder wall when the packing is in place in the pump. When such a packing is supported in a holding member and driven with the lip leading in the cylinder during the pressure stroke, it is common for the packing proximate to the cylinder wall to "balloon" within the necessary clearance space provided between the cylinder wall and the holding member. The "ballooning" causes the packing material to extrude toward the rear between the holding member and the cylinder wall. As a consequence, a high pressure spike appears between the packing and the cylinder wall at that point near the rear portion, or the heel, of the contact area. The packing material is worn away in the heel area due to the high pressure, the "ballooning" tendency is increased due to the weakened packing in the heel area and additional packing material migrates to the heel of the contact area, thus accelerating wear. Severe localized wear patterns are observed at this portion of the contact area due to the high contact pressure. There is generally little or no contact pressure in the area at the forward lip of the cup shaped packing due to initial deformation of the packing material which causes the lip to separate from the cylinder wall when fitted within the pump cylinder. The high localized contact pressure and accelerated wear in the heel area soon requires packing replacement due to the excessive localized wear.
It is apparent that a packing cup with structural characteristics which will reduce the extrusion tendency and provide a more uniform pressure across the contact area between the packing and the cylinder wall would be desirable from the standpoint of decreasing the rate of packing wear and thereby increasing the packing life.